For example:

Column Q could contain 500 rows most of which are numbers, some are text, and I want to total up only the numbers, BUT I only want to total the numbers in this column if coloumn G meets a certain criteria, usually the name of a company, and the numbers referring to customers with that company.

So far I've tried several variations on the formula below

{=SUBTOTAL(IF(9,'APRIL 2010 DATA'!$Q$3:$Q$999)*('APRIL 2010 DATA'!$G$3:$G$999=A5))}

Thanks for your help